Amorphous hydrogenated carbon (a--C:H), also known as diamond-like carbon (DLC) because of its hardness, has many useful properties such as chemical inertness, high wear resistance, high resistivity, and low dielectric constant (k&lt;3.2) such as described by Meyerson et al. in U.S. Pat. No. 4,647,494 which issued Mar. 3, 1987, Grill et al. in U.S. Pat. No. 5,462,784 which issued Oct. 31, 1995 and A. Grill and B. S. Meyerson, "Development and Status of Diamond-like Carbon", Chapter 5, in Synthetic Diamond: Emerging CVD Science and Technology, editors K. E. Spear and J. P. Dismukes, John Wiley and Sons, New York 1994. DLC films can be fabricated by a variety of methods including sputtering, ion beam sputtering, and dc or rf plasma assisted chemical vapor deposition with a variety of carbon-bearing source materials such as described above and by F. D. Bailey et al. in U.S. Pat. No. 5,470,661 which issued Nov. 28, 1995.
A number of useful DLC analogues may be synthesized by replacing some of the carbon or hydrogen in the a--C:H with other elements. For example, silicon-containing diamond-like carbon (SiDLC), a DLC analogue with 5-10% C replacement by Si, has a much higher resistance to oxygen-based reactive ion etching (RIE) than unmodified DLC. Fluorinated diamond like carbon (FDLC or a--C:F:H), a DLC analogue in which some or most of the H is replaced by F, has lower stresses than DLC as well as a lower dielectric constant (k&lt;2.8). Other additives to DLC or FDLC may include nitrogen, oxygen, germanium, and metallic elements.
The low dielectric constants of DLC and FDLC make them potentially useful as insulator materials in high performance VLSI and ULSI chips where interconnect wiring capacitance must be minimized. This use for DLC and FDLC is discussed by S. A. Cohen et al. in U.S. Pat. No. 5,559,367 which issued Sep. 24, 1996, entitled "Diamond-like carbon for use in VLSI and ULSI interconnect systems." However, these diamond-like materials can have high stresses and can change dimensionally after heating, making them difficult to use in their as-deposited form. For example, the high stresses in as-deposited DLC films can be high enough to produce a wafer bowing that interferes with lithography. Furthermore, since fabrication of back-end-of the line (BEOL) interconnect structures typically includes a final passivation anneal at 400.degree. C. for 4 hours, insulators used in these structures must be stable to such treatment.
A common requirement for film stability is that film weight loss per hour be less than 0.5% at a selected temperature at or below 400.degree. C. The use of films not meeting this requirement may cause a number of problems in BEOL interconnect structures. Annealing-induced film shrinkage or expansion may change the final film dimensions, or in constrained films, put unacceptable stresses on the wiring structures. Film decomposition products produced during annealing may outgas and produce delamination and/or cracking, especially in multilayer structures.
While film thermal stability may be improved by adjusting the deposition conditions, such improvements typically come with the expense of undesirably higher dielectric constants, as reported by Grill et al. in "Diamond-like carbon materials as low epsilon dielectrics for multilevel interconnects in ULSI", Mat. Res. Soc. Symp. Proc. 443 xxx (1997).
It is thus an object of this invention to provide a method for stabilizing carbon-based insulating films such as DLC and FDLC.
It is a further object of this invention to provide a stabilization method that is effective and economical in time and cost.
It is still a further object of this invention to provide a stabilization method which may also act to lower the dielectric constant of carbon-based insulating films such as DLC and FDLC.